Well, nobody else has mentioned it, but I'll throw in my oddball $.02 worth...
Wear oversize safety glasses, a baseball cap (or western Stetson if you are in Occupied Mexico), and a shirt that you can button up the collar fairly snug...
It's been my experience that Luger P-08's/LP-08's, Mauser C96's/M30's, and Nambu T-14's eject fired cartridge cases straight up and back...Most of mine hit me square in the forehead, but several friends have gotten hot cases down their necks...